Is A Major U.S. Dam At Its Breaking Point?

Stretching a mile from end to end, the gigantic Wolf Creek Dam is vital to southern Kentucky and northern Tennessee, preventing the periodic flooding that once plagued the cities and towns along the 700 mile Cumberland River. But Wolf Creek Dam is in trouble.

"The problem is about 250-300 feet below us in the rock," says Mike Zoccola.

Zoccola is with the Army Corps of Engineers, which recently designated the dam at "high risk" for failure, requiring "emergency measures" to reduce an "imminent risk of human life".

"We estimated a range somewhere between about 50 and 120 people, the loss of life — people who live downstream, and possibly fishermen or campers that may be down there," he tells CBS News transportation and consumer safety correspondent Nancy Cordes.

The devil is in the design. Wolf Creek Dam was built on porous limestone. Over time, water has seeped into cracks in the rock, eroding a Swiss cheese of holes and caves. A sinkhole could cause this entire earthen embankment to collapse.

Cordes Blogs: Dangerous Dams
The first town downstream is Burkesville, Ky. The state has handed out warning radios to all 1,700 residents.

"Have they told you how much time you'd have to get out if this thing went off?" asks Cordes.

"I've heard 4 to 6 hours," a restaurant manager said.

There are currently 3,500 dams in the United States listed as unsafe and the list is growing faster than the rate of repair. They may not all be as big as Wolf Creek Dam, but when they fail, the results can be catastrophic.

In recent years, fears about dams giving way have forced evacuations in Maryland, Massachusetts and Missouri. Seven lives were lost last year when a dam broke in Hawaii.

The American Society of Civil Engineers gives the infrastructure report cardnation's dams a "D" and called for fully funded dam safety programs in all 50 states.

"If you live downstream from the dam, it doesn't matter whether the dam was attacked by terrorists or whether it failed because of fatigue and age and lack of repair. The people downstream are all impacted the same," says Patrick Natale of the American Society of Civil Engineers.

At Wolf Creek Dam, lake levels have been lowered to reduce pressure and crews are working 24 hours-a-day to fill the underwater holes with grout.

Because while the potential damage to Burkesville would be in the millions, the damage to Nashville, Tenn., located further downstream, would be measured in the billions.

Tomorrow we take a look at the state of America's levees. Two years after Hurricane Katrina, many of them are being pushed to the brink.